As we continue, we begin by describing a new design keyword:
We'll also introduce introduce one new piece of object syntax.
But first, let's warm up with another graded debugging challenge!
this is a keyword in Java that you can use in your instance methods.
It always refers to the current instance that is executing the method.
is equivalent to this:
The example above is one use of
However, we'll usually just go the first route, and choose parameter names that don't conflict with our instance variable names.
This helps avoid mistakes.
checkstyle will help you with this, complaining (as it does above) that your parameter "hides a field".
However, there is one place where we will use
Let's go through it together:
The object methods we have been writing so far are known as instance methods:
Even though they share the same implementation, you can think of each
Person as having its own
that can access its instance variables, in this case
However, Java also allows us to create methods that are attached to the class, not to the instance.
To do that, we use a new keyword:
Let's see how that works:
static class methods cannot access instance variables.
Let's look at why, and the differences between class and instance methods:
static class methods are not uncommon.
Particularly when you have methods that don't need an instance to function properly.
Let's look at one example of a class that consists almost entirely of
You can also use the
static keyword on fields.
One common use for this is to establish constants to make our code more readable and less error-prone.
To do this, we combine
static with a keyword that we haven't seen before,
final creates a variable that cannot be changed after it has been set.
We can combine
final to create a symbolic constant.
Let's look at how:
Can you create modifiable—that is, non-
This is extremely rare, and very easy to get wrong.
We won't test you on it, but view this walkthrough to see how this works:
Need more practice? Head over to the practice page.